NEW YORK — At least the Celtics enter Monday night’s challenge against the Knicks at Madison Square Garden feeling better about themselves, an improvement over a week ago, when the Kings embarrassed them with seven 3-pointers in the fourth quarter.

Who would have believed that six days later, the Celtics would hold a team to seven field goals in a half, as they did Saturday night against the Hawks at Philips Arena? Who would have thought the Celtics would be able to so dominate a game defensively, as they also did Friday against the Pacers?

When the Celtics are in a defensive flow, when they are communicating, when they are in synch, you can see confusion from the opposing team. The Hawks spent the second half of the Celtics’ 89-81 victory with an “uh-oh” feeling, whipping the ball around as if it were a grenade. It was reminiscent of the Celtics’ not-too-distant, glorious past.

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For the season’s first 31 games, they exhibited little of that play. For the last two, in which they have allowed an average of 78 points, they have displayed greater intensity.

In the four quarters against Indiana and the final two against Atlanta, the Celtics held their opponent to 30 percent shooting, 7 of 31 on 3-pointers, and forced 33 turnovers.

“We’re starting to commit ourselves toward the defensive end,” Kevin Garnett said. “A [good] defense takes a lot of energy, takes grit, takes commitment, and each guy is willing to do just that. These last two games we’ve been firm, aggressive, really going for steals. That starts with [Rajon] Rondo and Avery [Bradley].

“Avery coming back has given us a sense of pressure on the ball, which helps the bigs pressure up. The different schemes that Doc [Rivers] and [assistant coach] Mike [Longabardi] are coming with are actually helping. We’re getting to some of the old, traditional stuff that we’ve done while I’ve been here, and it’s working.”

It may have begun with simply being more forceful. It’s no coincidence that in the last two games the Celtics have been involved in a few dust-ups. Garnett had a few exchanges with Indiana’s Tyler Hansbrough, before being ejected with 8:24 left because of a Flagrant-2 foul, with Garnett obviously trying to send a physical message.

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On Saturday, the Celtics refused to relent on loose balls, and Garnett got into a brief altercation with Atlanta’s Anthony Tolliver.

“We’re scrappy as [expletive] right now,” he said. “We’re trying to get wins here and the only way we’re going to get them is sometime you’ve got to go and take them.”

The key to Saturday’s game was containing Hawks guards Lou Williams and Jeff Teague, who combined to go 14 for 20 in the first half for 34 points, including five 3-pointers. In the second half, they were 2 for 6 for 11 points and one 3-pointer.

“I just told Avery, we’ve got to do a better job with the guards. Our bigs were handling Al [Horford] and Josh [Smith], but we let Teague and Williams get loose easy,” said Rondo. “So we stayed back [in the locker room at halftime] and watched a little more film, and said, ‘Let’s turn it up a little bit.’ ”

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The Celtics waived second-round pick Kris Joseph and recently signed Jarvis Varnado, according to an NBA source, ahead of this week’s deadline to guarantee all contracts.

Joseph had gone back and forth between the Celtics and the Development League, and was in Maine when the move was made. Joseph averaged 17.7 points and 5.3 rebounds in 10 games for the Red Claws. Varnado was added to the roster when the Celtics lost Chris Wilcox to a sprained wrist, but he played sparingly.

Joseph could return under a 10-day contract or is eligible to sign with another club once he clears waivers on Monday. The Celtics now have 13 players, giving them roster flexibility if they decide to make a trade or add a free agent.

The team is seeking a legitimate defensive center to pair with Garnett.